Numerical investigation of the flow evolution of an oscillating foil with the different reduced frequency

The power extraction systems based on oscillating foil are played more and more attention in alternative energy extraction systems. The dynamic stall problem on oscillating foil is related to general performance of energy extraction systems, where a varying flow filed is introduced by a rapid change in the effective angle of attack. The objective of this paper is to investigate the flow evolution of an NACA0012 foil undergoing sinusoidal pitching motion with the different reduced frequency. The k-ω SST turbulence model, coupled with a two-equation γ-Reθ transition model, is used for the turbulence closure. The results showed that the numerical method can well capture the dynamic stall process. With the increasing of the reduced frequency, the dynamic stall is delayed during the development of the Leading Edge Vortex stage. During post-stall vortex shedding stage, the mechanism of post-stall vortex shedding present different style at different reduced frequency K. When K=0.1, the secondary vortex forms and covers the whole suction face again along with the shedding of LEV. Compared to the case of K=0.1, no secondary vortex was induced for K=0.05. However, When K=0.2, the secondary vortex covers the whole suction surface again because the oscillating velocity is too fast to develop the secondary vortex.